1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a semiconductor device having a chip electrically connected to a substrate.
2. Description of the Related Art
FIG. 1 shows a cross-sectional view of a conventional semiconductor device. The conventional semiconductor device 1 comprises a substrate 2, a chip 3 and an underfill 36. The substrate 2 has a first surface 21, at least one substrate pad 22 and a solder mask 23. The substrate pad 22 is disposed adjacent to the first surface 21. The solder mask 23 is disposed adjacent to the first surface 21, and has at least one solder mask opening 231 so as to expose part of the substrate pad 22. The chip 3 is disposed adjacent to the first surface 21 of the substrate 2, and is electrically connected to the substrate 2. The chip 3 comprises a chip body 31, at least one chip pad 32, a first passivation 33, an under ball metal layer 34 and at least one bump 35. The chip body 31 has an active surface 311. The chip pad 32 is disposed adjacent to the active surface 311. The first passivation 33 is disposed adjacent to the active surface 311, and has at least one first opening 331 so as to expose part of the chip pad 32. The under ball metal layer 34 is disposed adjacent to the chip pad 32. The bump 35 is disposed adjacent to the under ball metal layer 34, and contacts the substrate pad 22 of the substrate 2. The bump 35 contacts the under ball metal layer 34 to form a first contact surface 351. The bump 35 contacts the substrate pad 22 of the substrate 2 to form a second contact surface 352. The underfill 36 encapsulates part of the active surface 311 of the chip 3 and the bump 35 of the chip 3.
The conventional semiconductor device 1 has the following disadvantages. A reliability test is conducted to make sure that the yield rate of the conventional semiconductor device 1 achieve a predetermined standard after it undergoes a great change in temperature. However, the coefficients of thermal expansion of every component of the conventional semiconductor device 1 are different, so the bump 35 endures a shear stress due to the expansion or contraction of its surrounding components. Moreover, if the first contact surface 351 or the second contact surface 352 has a relative weak bonding force, a crack 37 will easily occur between the bump 35 and the contact surface which has a relative weak bonding force.
Therefore, it is necessary to provide a semiconductor device to solve the above problems.